Milk sterilizing apparatus

ABSTRACT

A sterilizing apparatus for fluent materials, particularly milk, for raising the temperature of the material to a sterilizing temperature in a very short period of time and then discharging the material for substantially instantaneous cooling to enable the sterilization to occur without adverse affect on the natural flavor and stability of the milk or other material. The sterilizing apparatus includes a pressure vessel communicated with a steam source and also includes a milk inlet pipe which introduces milk into the vessel through insulated distribution pipes for equal volume inlet through a plurality of horizontally disposed slot-like openings so that the milk will be discharged into the vessel in the form of a plurality of thin films. A depending screen may be provided in each of the slot-like openings so that milk will be discharged along the surface of the screen to form a thin film and assure that each particle of milk is identically heated to ensure complete sterilization. The bottom of the pressure vessel is coated with an inert plastic material to prevent any buildup of milk on such surfaces. The bottom of the pressure vessel is communicated with a source of vacuum through a liquid seal and a holding tube with the holding time and length being factors so that the sterilized milk will be instantaneously cooled from its sterilizing temperature. The stream which is introduced into the pressure vessel is absorbed into the milk as it is heated and the steam that was added to the milk during the heating and sterilization process will be removed therefrom during the cooling process.

United States Patent 1 1 Davies Nov. 13, 1973 MILK STERILIZING APPARATUS[75] Inventor: Elmer S. Davies, Takoma Park,

[73] Assignee: Dasi Industries Inc., Washington,

221 Filed: July 3,1972

21 Appl. No.: 268,873

Primary Examiner-Robert W. Jenkins Att0rney--l-larvey B. Jacobson et al.

[57] ABSTRACT A sterilizing apparatus for fluent materials, particularlymilk, for raising the temperature of the material to a sterilizingtemperature in a very short period of time and then discharging thematerial for substantially instantaneous cooling to enable thesterilization to occur without adverse affect on the natural flavor andstability of the milk or other material. The sterilizing apparatusincludes a pressure vessel communicated with a steam source and alsoincludes a milk inlet pipe which introduces milk into the vessel throughinsulated distribution pipes for equal volume inlet through a pluralityof horizontally disposed slotlike openings so that the milk will bedischarged into the vessel in the form of a plurality of thin films. Adepending screen may be provided in each of the slotlike openings sothat milk will be discharged along the surface of the screen to form athin film and assure that each particle of milk is identically heated toensure complete sterilization. The bottom of the pressure vessel iscoated with an inert plastic material to prevent any buildup of milk onsuch surfaces. The bottom of the pressure vessel is communicated with asource of vacuum through a liquid seal and a holding tube with theholding time and length being factors so that the sterilized milk willbe instantaneously cooled from its sterilizing temperature. The streamwhich is introduced into the pressure vessel is absorbed into the milkas it is heated and the steam that was added to the milk during theheating and sterilization process will be removed therefrom during thecooling process.

14 Claims, 6 Drawing Figures United States Patent Davies NOV. 13, 1973 l56 I. I

O O O 74 1 I0 I l) v 54 66 oo 35 72 Q o is O 00 ?0 7'6 //2 PATENTEU NOV1 3 I975 SHEET 16F 3 VAC CHAMBER STERILIZER HOMOGENIZER MILK SUPPLYFREHEATER OR PUMP Fig.4

MILK STERILIZING APPARATUS BACKGROUND OF THE INVENTION 1. Field of theInvention The present invention generally relates to a milk sterilizingapparatus and more particularly, such an apparatus which willeffectively heat the milk to a sterilizing temperature in a very shorttime without disturbing its natural flavor and stability andsubsequently instantaneously cooling the sterilized milk from itsterilizing temperature with the entire sterilizing process requiring avery short elapsed time.

2. Description of the Prior Art My prior U. S. Pat. No. 2,899,320,issued Aug. 11, 1959 discloses a process for the sterilization of milkin which preheated milk is introduced into a sterilizer where it israised to a sterilization temperature and then discharged into a vacuumchamber for cooling. The apparatus schematically disclosed in thispatent has been subsequently improved to provide a more effectivesterilization of the milk. Prior U. S. Pat. No. 3,032,423 discloses anapparatus for forming a thin film of milk within a pressure vessel forsterilization thereof but fails to provide an adequate structure andnecessary control for the incoming milk and the discharged milk which isinstantaneously cooled. Prior U. S. Pat. No. 1,819,023, issued Aug. 18,1931 also discloses a process and apparatus for thermal sterilization ofmilk. This patent employs a violent agitation or turbulence of the milkparticles which has been found to result in adverse affects upon thesterilized milk product.

Prior U. S. Pat. No. 2,115,472, issued Apr. 26, 1938 discloses a milksterilizing apparatus which also attempts to quickly heat the milk andthen rapidly cool the milk. Also, in this patent, the steam isintroduced into the milk by a jet action which creates a high degree ofagitation or turbulence in the milk which has been found to result inadverse affects upon the sterilized milk product.

Prior U. S. Pat. No. 2,049,591 discloses a process of sterilizing milkby heating the milk to a sterilizing temperature and then introducingthe milk into sterilized containers where it is held at an elevatedtemperature for a period of time. This patent fails to disclose anyparticular apparatus for carrying out the process disclosed.

While the prior art discloses the basic process of sterilizing milk byrapidly heating it to a sterilizing temperature and then rapidly coolingit and includes apparatuses for accomplishing this function, suchdevices have not been successfully utilized on a commercial basis dueprobably to deficiencies in the quality of th sterilized milk productand probably due to inefficiencies in operation of the apparatus.

SUMMARY OF THE INVENTION An object of the present invention is toprovide a mill sterilizing apparatus in which milk, under pressure, canbe raised to a sterilizing temperature within a very short time anddischarged for substantially instantaneous cooling in order to sterilizethe milk without disturbing its natural flavor and stability with theapparatus controlling the passage of milk through the sterilizer so thatno particle of the milk comes in contact with any surface that issubstantially hotter than the milk itself with the milk being dischargedinto the apparatus in a plurality of downwardly directed thin filmsseparated from each other and being subject, during its downward travel,to direct contact with steam that is at a sufficient temperature andpressure to raise each and every particle of the milk to the sterilizingtemperature with the steam and milk being combined during the heatexchange process.

A further object of the invention is to provide a milk sterilizingapparatus in which the pressure vessel into which the milk is dischargedand into which the steam is discharged is provided with a liquid seal inthe bottom thereof so that the liquid effluent is discharged into avacuum container where the effluent is quickly reduced in temperaturewhich result in substantially instantaneous cooling of the milk andseparation of water therefrom with very little, if any, denaturation ofthe milk thereby preventing any off taste in the sterilized milkproduct.

Still another object of the invention is to provide a milk sterilizingapparatus which effectively controls the time-temperature relationshipfrom the time the milk enters the pressure vessel or sterlizing chamberuntil it passes into the vacuum chamber or container in an efficientmanner with the structure being relatively simple, easy to install andmaintain in a sterile condition and yet relatively inexpensive tooperate and to maintain.

These together with other objects and advantages which will becomesubsequently apparent reside in the details of construction andoperation as more fully hereinafter described and claimed, referencebeing had to the accompanying drawings forming a part hereof, whereinlike numerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of thesystem incorporating the milk sterilizing apparatus of the presentinvention therein.

FIG. 2 is a side elevational view of the sterilizing apparatusillustrating the device in open condition.

FIG. 3 is a vertical sectional view of the sterilizing apparatus, on anenlarged scale, illustrating the specific structural details thereof.

FIG. 4is a plan sectional view taken substantially upon a plane passingalong section line 44 of FIG. 3 illustrating further structural detailsof the sterilizing apparatus.

FIG. 5 is a transverse, plan sectional view taken substantially upon aplane passing along section line 55 of FIG. 3 illustrating furtherstructural details of the pressure vessel.

FIG. 6 is a detailed sectional view of one of the discharge pipes forthe milk illustrating the slot-like construction and screen to provide athin milk film.

DESCRIPTION OF THE PREFERRED EMBODIMENT The milk sterilizing apparatusof the present invention is generally designated by reference numeral 10and is schematically illustrated in a milk sterilizing system in FIG. 1which includes a milk supply 12 and a preheater 14 to preheat the milkto approximately F. which will prevent whey protein denaturation. Fromthe preheater, the milk is passed through a homogenizer 16 or pump andthrough a diversion valve 18 which communicates with the milk inlet pipe20 of the sterilizing apparatus and a diversion line 22 which extendsback to the inlet of the homogenizer or pump 16. As the milk passesthrough the homogenizer, it is increased in temperature by approximately5F. due to the pressure in the homogenizer so that milk entering themilk sterilizing apparatus will be at approximately 160F.

The milk inlet pipe is in the form of a manifold having a plurality ofdownwardly extending pipes 24 communicated therewith. The terminal endof the inlet pipe 20 is provided with a closure cap 26 with the endmostdownwardly extending pipe 24 being disposed closely adjacent the endcap. Each of the downwardly extending pipes 24 is provided with aregulating valve 28 and a pressure gauge 30. The lower part of eachinlet pipe 24 extends downwardly into a cylindrical jacket 32 having anupper closure cap 34 thereon with the pipe 24 being spaced from thejacket 32 and insulated therefrom by an insulating material 38.

The lower end of the inlet pipe 24 is communicated with a'transverselyextending milk discharge pipe 24 that is enclosed by a horizontallydisposed tubular member 44 which encircles the pipe 42 in eccentricrelation thereto with the space between the tubular member 44 and thedischarge pipe 42 being filled with insulation 46. The lower peripheryof the discharge pipe 42 is provided with a relatively narrow slot 48extending throughout the length thereof for discharging milk in a thinfilm through a wider slot 50 in the tubular member 44. To furtherfacilitate maintaining the milk discharge in a thin film, a screen panel52 is supported from the tubular member 44 in alignment'with the slot 50and the slot 48 so that the milk discharged will be discharged along thesurfaces of the screen to maintain the thin film characteristicsthereof.

All of the aforementioned components are mounted on the upper half orlid portion 54 of a sterilization chamber or pressure vessel 56 whichmay by cylindrical in construction and provided with reinforcing rings58 and 60 at the lower edge of the lid or dome 54 and the upper edge ofthe vessel 56 as illustrated in FIG. 3. The reinforcing rings 58 and 60are releasably secured together by suitable fastening devices 62 and aseal 64 of any suitable type is provided for sealing the lid or dome 54and the vessel 56 when in closed condition. A suitable hinge structure66 is provided for supporting the lid from the vessel and acounterweight 68 may be provided for counterbalancing the lid weight tofacilitate cleaning of the apparatus by maintaining the lid or dome inan open condition as illustrated in FIG. 2.

The vessel 56 includes an inner cylindrical wall 70 surrounded by amanifold 72 communicated with a steam inlet pipe 74. A plurality ofapertures 76 communicates the manifold 72 with the interior of thevessel 56. The lower end of the wall 70 is provided with a conicalmember 78 in the form of a collection chamber which is coated with acoating of inert plastic material 80 such as Teflon or any other similarmaterial. The lower end of the conical shaped collection chamber ormember 78 is communicated with a discharge pipe 82 which is incommunication with a vacuum chamber 84. The discharge line 82 isprovided with a liquid level control valve assembly 86 that controls thediverter valve 18 in a manner to conform the discharge volume with theintake volume to maintain a constant flow through the sterilizer andprevent variable flow rate that could result in retention of anexcessive volume of milk in the sterilizer beyond the desiredtimetemperature conditions. Steam is introduced into the being diffusedand coming into intimate contact with' the milk films to evenly heat allparticles of milk to the same temperature with the steam being absorbedby the milk and the desired temperature being 300F. with the liquidseal, formed by the control valve apparatus 86, retaining thistemperature for 0.5 second with the heated milk taking 1 second to passthrough the pipe to the vacuum chamber where the temperature drops to160F. instantaneously.

The lower conical portion of the pressure vessel 56 is provided with aconical jacket 88 which is spaced from and generally parallel to theconical member 78 and which defines a conical annular space 90therebetween for flow of a coolant such as water or air with the coolantentering the bottom of the jacket 88 through inlet lines 92 and exitingfrom the jacket at the upper end thereof by discharge lines or conduits94. As illustrated in FIG. 5, the jacket 90 is divided into twodiametric areas by baffles 96 which are diametrically opposed and whichextend from the top to the bottom of the jacket for separating thejacket into two halves each of which is provided with an inlet conduit92 and an outlet conduit 94. Each half of the jacket 90 is provided witha plurality of baffles 98 alternate of which extend from the top of thechamber down to a point spaced above the bottom of the chamber with theadjacent baffle extending from the bottom of the chamber up to a pointspaced below the top of the chamber thereby defining a tortuous orzigzag path of flow for the coolant. Temperature responsive controldevices are provided for controlling the coolant flow through thecooling jacket 90 for maintaining the temperature of the conical member78 at a predetermined temperature level to avoid the possibility of thetemperature of the conical member 78 becoming hotter than the milk whichcould result in the milk sticking onto or coating the inner surfacethereof.

The dome 54 is provided with a cleaner spray head 100 communicated witha supply pipe or conduit 102 which is connected with a suitablepressurized supply for a cleaning solution so that the interior of thesterilizer may be cleaned without opening the device. The cleaningsolution, of course, isdirected to a collecting tank or recirculated bythe use of a detachable hose connection or other detachable pipeconnection or valved T-connection at the lower discharge end of thesterilizer. When a more thorough cleaning may be desired, the dome 54may be opened and cleaned using accepted cleaning procedures. Also, thedome 54 has a discharge pipe 104 provided with a valve 106 therein whichmay be employed to purge air from the interior of the sterilizer whencommencing operation thereof after cleaning. Also, the dome is providedwith a covering surface 108 defining a jacket for insulation 110 toserve to restrict the loss of heat from the sterilizer A similar jacket1 12 is provided for the pressure vessel 66 which encloses the manifold72 and defines the upper end of the cooling jacket 90 as illustrated inFIG. 3.

Th screen 52 may be supported in relation to the discharge pipe 42 byhaving the upper edge thereof reversely folded at 53 so that it will beretained in position but stillenable discharge of milk through the slotsalong the screen surface. At least one end of the slots will be opensufficiently to enable the screen to be slid inwardly with the reversebend 53 disposed interiorly of the discharge pipe 42 with the open endof the slots being effectively closed by the end portion of the screen.

in cleaning the interior of the inlet pipes and associated structure, acleaning solution conduit is connected to the inlet pipe in any suitablemanner so that the cleaning solution will be used not only to clean theinterior surfaces of the inlet pipes but also the exterior surfaces ofthe sterilizer which are exposed to milk during the sterilizationprocess.

In actual practice, the temperature of the steam within the sterilizeris maintained at 310F. and 64 psig. The coolant flow is controlled tomaintain temperature of the conical member 78 at 300F. This temperaturemay be controlled by suitable sensing devices associated with thecoolant outlet and inlet and suitable control valves to maintain thetemperature of the conical member 78 at the desired level. Thetemperature and pressure conditions are maintained through the liquidseal at the lower end of the chamber 78 and the discharge pipe 82 untilthe effluent reaches a temperature-pressure valve 1 16 that dischargesdirectly into the bottom of the vacuum chamber 84 which has the upperend thereof communicated with a vacuum source 118 with the vacuum sourcemaintaining the vacuum chamber under predetermined vacuum conditions. Asthe effluent is discharged through the temperature and pressureregulating valve 116 into the vacuum chamber 84, it is instantaneouslylowered in temperature and pressure to 160F. and 28% inches Hg. whichnot only instantaneously lowers the temperature but also sepa rateswater from the milk. The control valve 86 may be of the diaphragm typeand is controlled to assure a liquid seal in the bottom of the chamber78 with temperature snesors in this area of the sterilizer also servingto control the diversion valve 18 and temperature sensors in the inletline 20 also serving to control the diversion valve 18 to assure thatthe milk entering the sterilizer will be at l60F. and that the volume ofmilk entering the sterilizer will be controlled so that the inlet volumewill be maintained so that the milk will be raised to 300F. in thesterilizer.

As an alternative arrangement, a strip of plastic material, such asTeflon" provided with spaced spherical balls along the top edge may beused in the slot in lieu of the screen 52 with the strip beingapproximately 2 inches in width with the thcikness being sufficientlyless than the width of the slot to provide an effective slot width of0.010 inch.

The foregoing is considered as illustrative only of th principles of theinvention. Further, since numerous modifications and changes willreadily occur to those skilled in the art, it is not desired to limitthe invention to the exact construction and operation shown anddescribed, and accordingly all suitable modifications and equivalentsmay be resorted to, falling within the scope of the invention.

What is claimed as new is as follows:

1. A sterilizing apparatus for milk and the like comprising a pressurevessel, a milk inlet pipe communicated with the upper portion of thevessel, at least one horizontally disposed milk discharge pipe disposedinteriorly of the vessel above the bottom thereof and in communicationwith the inlet pipe, said discharge pipe including a longitudinallyextending, relatively narrow slot in the bottom portion thereof fordischarging milk in the form of a thin film, steam inlet meanscommunicating with the interior of the pressure vessel for dischargingsteam into the interior thereof at a predetermined temperature andpressure for heat exchange association and absorption by the thin filmof milk for rapidly heating all particles of the thin film of milk to 5sterilizing temperature without substantial agitation of the milk, anddischarge conduit means including a liquid seal at the bottom of thevessel for discharge of the effluent to a vacuum chamber forinstantaneous cooling of the sterilized milk from the sterilizingtemperature.

2. The structure as defined in claim 1 wherein said steam inlet meansincludes a manifold encircling the vessel and a plurality ofcircumferentially spaced inlet openings in the vessel communicating themanifold with the interior of the vessel to introduce the steam into thevessel through a relatively large area to maintain the velocity of theincoming steam at a minimum to reduce turbulence and agitation.

3. The structure as defiend in claim 1 wherein said dicharge conduitmeans includes a liquid level control, said milk inlet pipe incudingcontrol means associated therewith operative in response to the liquidlevel control to control the flow rate of milk so that a substantiallyconstant volume of milk flows through the presure vessel.

4. The structure as defined in claim 1 wherein the bottom portion of thevessel is in the form of a conical member having a sloping surfacetoward the center with the discharge conduit means being communicatedwith the bottom center of the conical member, the inner surface of theconical member being coated with an inert non-metallic material toreduce sticking of milk on the surface and facilitating cleaningthereof.

5. The structure as defined in claim 4 together with a jacket on saidconical member to receive a coolant, means communicated with the jacketfor circulation of the coolant to maintain the conical member at apredetermined temperature.

6. The structure as defined in claim 1 wherein said milk inlet pipe isprovided with a plurality of downwardly extending pipes disposed insubstantially vertical relation, each of the vertical milk inlet pipesincluding a horizontally disposed discharge pipe with a slot in thebottom thereof thereby discharging the milk in a plurality of thin filmsfor heat exchange with and absorption of the steam.

7. The structure as defined in claim 6 wherein each of the verticalpipes and each of the horizontal slotted pipes is provided withinsulation thereon to prevent heating of the pipes to a temperaturehigher than the milk.

8. The structure as defined in claim 7 together with a verticallydisposed screen panel in alignment with each discharge slot whereby milkdischarged from each slot will flow down over the surface of the screento assure equal heating of each particle of milk discharged into thevessel.

9. A sterilizing apparatus for liquid material comprising a pressurevessel, steam inlet means in said vessel to introduce steam into thevessel with a minimum of turbulence, liquid inlet means above the steaminlet means to discharge liquid into the vessel in a thin vertical filmwhereby the force of gravity causes downward How of the thin film ofliquid for direct contact with the steam for condensing and absorptionof the steam with the steam raising the temperature of the liquid to asterilizing temperature, vacuum discharge means commu coolant jacketmeans receiving circulating coolant to retain the pressure vessel at apredetermined temperature.

11. The structure as defined in claim 10 wherein said steam inlet meansincludes a manifold disposed peripherally of the vessel, and a pluralityof inlet apertures communicating the manifold with the interior of thevessel for reducing the velocityof incoming steam.

12. The structure as defined in claim 11 wherein said milk inlet meansincludes at least one horizontal tubular member having a discharge slottherein, and insulating means on the tubular member for insulating themilk from the steam prior to direct contact therebetween. I

13. The structure as defined in claim 9 wherein said liquid inlet meansincludes a plurality of horizontally disposed tubular members, each ofsaid tubular members having a longitudinal slot in the bottom thereoffor discharging a plurality of thin films of liquid.

14. The structure as defined in claim-l3 wherein each of said slotsincludes a depending strip to form a surface on which the thin film ofliquid is formed.

1. A sterilizing apparatus for milk and the like comprising a pressurevessel, a milk inlet pipe communicated with the upper portion of thevessel, at least one horizontally disposed milk discharge pipe disposedinteriorly of the vessel above the bottom thereof and in communicationwith the inlet pipe, said discharge pipe including a longitudinallyextending, relatively narrow slot in the bottom portion thereof fordischarging milk in the form of a thin film, steam inlet meanscommunicating with the interior of the pressure vessel for dischargingsteam into the interior thereof at a predetermined temperature andpressure for heat exchange association and absorption by the thin filmof milk for rapidly heating all particles of the thin film of milk tosterilizing temperature without substantial agitation of the milk, anddischarge conduit means including a liquid seal at the bottom of thevessel for discharge of the effluent to a vacuum chamber forinstantaneous cooling of the sterilized milk from the sterilizingtemperature.
 2. The structure as defined in claim 1 wherein said steaminlet means includes a manifold encircling the vessel and a plurality ofcircumferentially spaced inlet openings in the vessel communicating themanifold with the interior of the vessel to introduce the steam into thevessel through a relatively large area to maintain the velocity of theincoming steam at a minimum to reduce turbulence and agitation.
 3. Thestructure as defiend in claim 1 wherein said dicharge conduit meansincludes a liquid level control, said milk inlet pipe incuding controlmeans associated therewith operative in response to the liquid levelcontrol to control the flow rate of milk so that a substantiallyconstant volume of milk flows through the presure vessel.
 4. Thestructure as defined in claim 1 wherein the bottom portion of the vesselis in the form of a conical member having a sloping surface toward thecenter with the discharge conduit means being communicated with thebottom center of the conical member, the inner surface of the conicalmember being coated with an inert non-metallic material to reducesticking of milk on the surface and facilitating cleaning thereof. 5.The structure as defined in claim 4 together with a jacket on saidconical member to receive a coolant, means communicated with the jacketfor circulation of the coolant to maintain the conical member at apredetermined temperature.
 6. The structure as defined in claim 1wherein said milk inlet pipe is provided with a plurality of downwardlyextending pipes disposed in substantially vertical relation, each of thevertical milk inlet pipes including a horizontally disposed dischargepipe with a slot in the bottom thereof thereby discharging the milk in aplurality of thin films for heat exchange with and absorption of thesteam.
 7. The structure as defined in claim 6 wherein each of thevertical pipes and each of the horizontal slotted pipes is provided withinsulation thereon to prevent heating of the pipes to a temperaturehigher than the milk.
 8. The structure as defined in claim 7 togetherwith a vertically disposed screen panel in alignment with each dischargeslot whereby milk discharged from each slot will flow down over thesurface of the screen to assure equal heating of each particle of milkdischarged into the vessel.
 9. A sterilizing apparatus for liquidmaterial comprising a pressure vessel, steam inlet means in said vesselto introduce steam into the vessel with a minimum of turbulence, liquidinlet means above the steam inlet means to discharge liquid into thevessel in a thin vertical film whereby the force of gravity causesdownward flow of the thin film of liquid for direct contact with thesteam for condensing and absorption of the steam with the steam raisingthe temperature of the liquid to a sterilizing temperature, vacuumdischarge means communicated with the pressure vessel through a liquidseal and a pressure-temperature regulating valve whereby discharge ofsteam with the liquid is precluded and the liquid and condensed steamwill be substantially instantaneously cooled and the condensed steamseparated from the liquid.
 10. The structure as defined in claim 9wherein the liquid is preheated milk, said pressure vessel includingcoolant jacket means receiving circulating coolant to retain thepressure vessel at a predetermined temperature.
 11. The structure asdefined in claim 10 wherein said steam inlet means includes a manifolddisposed peripherally of the vessel, and a plurality of inlet aperturescommunicating the manifold with the interior of the vessel for reducingthe velocity of incoming steam.
 12. The structure as defined in claim 11wherein said milk inlet means includes at least one horizontal tubularmember having a discharge slot therein, and insulating means on thetubular member for insulating the milk from the steam prior to directcontact therebetween.
 13. The structure as defined in claim 9 whereinsaid liquid inlet means includes a plurality of horizontally disposedtubular members, each of said tubular members having a longitudinal slotin the bottom thereof for discharging a plurality of thin films ofliquid.
 14. The structure as defined in claim 13 wherein each of saidslots includes a depending strip to form a surface on which the thinfilm of liquid is formed.